Exsolution Process Research Articles

Critical assessment of the exsolution process in Cu-doped SrTiO3 by a combined spectroscopic approach

Insights for an effective evaluation of copper exsolution in Cu-doped SrTiO3 have been obtained by combining classical techniques with EPR.

Regulating socketed geometry of nanoparticles on perovskite oxide supports for enhanced stability in oxidation reactions.

Heterogeneous catalysts with highly dispersed active particles on supports often face stability challenges during high-temperature industrial applications. The ex-solution strategy, which involves in situ extrusion of metals to form socketed particles, shows potential for addressing this stability issue. However, a deeper understanding of the relationship between the socketed geometry of these partially embedded nanoparticles and their catalytic performance is still lacking. Here, in situ transmission electron microscopy and theoretical calculations are utilized to investigate the oxygen-induced ex-solution process of Pd-doped LaAlO3 with varying concentrations of La vacancies (LaxAl0.9Pd0.1O3-δ). We find that the socketed geometry of Pd-based particles can be tuned by manipulating the levels of La deficiencies in the oxide support, which in turn influences the catalytic performance in high-temperature oxidation reactions. As for the socketed particles, the balance between particle size and outcrop height is crucial for determining the oxidation activity and sinter-resistance behavior. Consequently, the optimized catalyst, La0.8Al0.9Pd0.1O3-δ, exhibits superior catalytic performances, particularly high stability (still working after aging at 1000 °C for 50 h) and water resistance in various combustion reactions (e.g., CH4 oxidation and C3H8 oxidation).

From Mechanism Study to Catalyst Design: Exsolved Ru Nanocatalysts on Proton Conducitng Oxide for Efficient Ammonia Synthesis

Since it was revealed that the ammonia synthesis reaction is associated with the nitrogen adsorption energy, represented by a volcano plot, the catalysts placed near the peak of volcano plot, particularly ruthenium (Ru), have been actively investigated. For high efficiency of ammonia synthesis under mild conditions, the requirements of supported Ru catalysts are i) electron donating ability of supports (as promoters) that weakens the N≡N bond, ii) hydrogen absorption/desorption capability of supports to suppress H2 poisoning on Ru surface, iii) refractory property for maintaining high specific surface area of supports, and iv) the structurally robust and uniformly distributed Ru nanoparticles. However, the supported Ru catalyst that simultaneously fulfills all requirements above has yet been developed. Here we report a highly active exsolved Ru nanocatalyst supported on perovskite proton conducting oxide, BaCe0.55Zr0.3Y0.15O3-δ (BCZY), for ammonia synthesis at atmospheric pressure based on the understanding of exsolution mechanism.The supported catalyst, 5mol% Ru-added BCZY, BaCe0.5Zr0.3Y0.15Ru0.05O3-δ, was synthesized via solid state reaction using appropriate amount of oxide precursors. Analyses of XRD for crystal structure, TEM for microstructure observation, TGA for measurement of mass change against temperature, XPS for determination of oxidation state, BET for surface area measurement, and catalytic activity for quantifying ammonia synthesis rate were carried out.The exsolution is basically driven by reduction of oxide support, corresponding to the mass loss owing to the oxygen release. Thus, the decrease in mass directly associated with the Ru exsolution in a form of metal. Based on in situ TG profile at 1000oC under reducing atmosphere, it was verified that the Ru exsolution process is controlled by size-related strain, and the degree of exsolution can be effectively enhanced as the reduction time increases, e.g., from 1h to 20h. The exsolved Ru nanoparticles on proton-conducting oxide support formed by 20h reduction treatment at 1000oC had diameter of ~6 nm, and exhibited higher catalytic activity for ammonia synthesis reaction compared to exsolved Ru via 1h reduction treatment as well as the previously reported catalysts. The use of proton conducting oxide support, which has electron donating capability, structurally refractory property, and hydrogen absorption/desoprtion capability, could possibly be synergistic to boost the catalytic activity of exsolved Ru nanocatalyst. In this presentation, the details on exsolved Ru catalyst as a function of temperature, probable exsolution mechanism, and role of proton conducting oxide support will be further discussed.

Cu-Doped La0.3Sr1.7Fe1.5Mo0.5O6-σ Decorated with Exsolved Nanoparticles for the Improvement of Syngas Production in Solid Oxide Electrolysers

A major concern within modern society is the need to substitute the fossil fuels with more renewable sources of the energy. Chemical industry is one of major players in the field of the usage of the crude oil to produce more complex chemicals. Despite of being good source of carbon species, a dropping amount of the coal and oil is raising the questions for future solutions. Carbon dioxide can be promising and sustainable source of carbon, but its high C-O bond energy (806 kJmol-1) poses general problems in efficient utilization. The most common feedstock in chemical synthesis is the syngas, a mixture of H2 and CO, which can be simply processed into more complex molecules like e.g., methanol, dimethyl ether, or methane.Highly inert CO2 can be transformed into more valuable CO via, so called, Reverse Water-Gas Shift Reaction (RWGS). Even though there are couple proposed CO2 activation mechanisms, and knowledge on the reaction is quite high, the common issue is still proper selection of the catalyst for the reaction. In the surface redox mechanism Cu metal is being oxidized by CO2 to form Cu2O with the release of CO. After that, Cu+ ions are getting reduced back to metallic copper using surrounding H2. Solid Oxide Cells can become good source of ‘green’ hydrogen and, at the same time, perform direct electrolysis or chemical reduction of CO2. High temperature, at which SOECs are working, is beneficial from the point of Faradaic efficiency and CO2 conversion rate. Steam electrode of SOEC contains copious amount of nickel. It is also a well-known catalyst for many reactions, but in this case the electrodes are struggling under carbon-rich atmosphere. Therefore, an addition of different catalytic materials is needed. Commonly used are mixed catalytic heterogenous systems composed of Cu supported on oxide materials e.g., FexOy, MoO3, La2O3, and many more.In this study a series of catalysts for SOECs were fabricated based on the Cu-doped double perovskite structure able to exsolve intermixed Cu or Cu-Fe nanoparticles supported on the matrix lattice of La0.3Sr1.7Fe1.5Mo0.5O6-σdenoted as LSFM. The usage of LSFM compound as a matrix for Cu exsolution was based on the idea that it already consists of the oxides, which are currently utilized as the catalysts in RWGS. On the other hand, quite high mixed ionic-electronic conductivity may lead to even more enhanced electrochemical activity of the compound.The samples with varying Cu dopant level (5-20 mol.%) were synthesized via modified Pechini method maintaining fixed Fe:Mo ratio. Selected powders were processed into inks and screenprinted onto Ni-YSZ electrode. During the startup procedure of the SOEC, the catalysts were activated and the exsolution of metallic nanoparticles occurred. The powders and catalytic layers were characterized using XRD, SEM, and XPS techniques in both oxidized and reduced states. Doped compounds were able to exsolve metallic nanoparticles with the coverage density and size depending on the initial Cu amount in the lattice and the temperature of the reduction. Additional Temperature-Programmed Reduction and Oxidation (TPR/TPO) tests were performed to better understand the formation mechanism of surficial nanoparticles.SOECs equipped with additional layer of LSFM-Cu on the fuel electrode were examined for the performance in coelectrolysis mode under flowing H2O-CO2 with subsequent measurement of the outlet gases concentration using GC-MS. New layer altered the production of syngas concerning H2:CO ratio, yield, selectivity and conversion rates. The anchoring effect of the exsolution process causes higher integration of the nanoparticles compared to conventional catalysts produced via simple deposition and most likely limits the evaporation and surface diffusion of copper. LSFM-Cu can be promising material for increasing the efficiency of the SOECs. Acknowledgements This work was supported by a project funded by National Science Centre Poland, based on decision UMO-2021/43/B/ST8/01831 (OPUS 22).

Perovskites As Oxygen Evolution Reaction Catalysts for Alkaline Electrolysis: A Stable Alternative?

The sluggish nature of the Oxygen Evolution Reaction (OER) is responsible for a large efficiency penalty in alkaline electrolysis (AEL), with intensive research targeting more active and stable catalysts. Catalyst testing is typically carried out in RDE setups under mild conditions. Such tests are useful for evaluating the catalytic activity, but the results are seldom inter-comparable due to differences in electrode fabrication, microstructure, catalyst surface area, and test conditions. Furthermore, the material activity and stability at mild conditions does not represent the one at industrial conditions. Thus, testing the materials at industrial application conditions is crucial, i.e. at higher temperatures, e.g. 60-100°C, at concentrated KOH, e.g. 6-10M, and for longer times.Perovskites are an exciting group of materials as OER catalysts due to their reported high catalytic activities [1], and their tunable properties, allowing ample room for optimization and use of abundant elements. Even though many studies report the stability of perovskites under mild conditions and for durations of up to 2000h [2], the stability at industrial conditions is still in question. In this study, we tested the catalytic activity of La-based perovskites and others at industrial conditions. For better comparability, the tests are carried out on dense and polished pelettes with a well-defined surface area. Post-mortem analysis shows that the most researched materials are unstable at industrial conditions. However, one candidate showed excellent stability far beyond the commercial operation window, with only minor signs of degradation after 200h at 150°C, while possessing excellent intrinsic activity, with an overpotential of 240mV at 10mA/cm2 ECSA.Furthermore, perovskites are an excellent host for exsolution, which is the partial decomposition of the host material to form well-dispersed and anchored nanoparticles on the surface of the host. We have used the exsolution process to enhance the catalytic activity even further, and short-term stability tests confirm the presence of the exsolved particles after several hours of operation at industrial conditions. To the best of our knowledge, this study shows the first report of exsolved catalysts under industrial operating conditions.[1] Liu, L. B., Yi, C., Mi, H. C., Zhang, S. L., Fu, X. Z., Luo, J. L., & Liu, S. (2024). Perovskite Oxides Toward Oxygen Evolution Reaction: Intellectual Design Strategies, Properties and Perspectives. In Electrochemical Energy Reviews (Vol. 7, Issue 1). Springer Nature Singapore. https://doi.org/10.1007/s41918-023-00209-2[2] Jo, H., Yang, Y., Seong, A., Jeong, D., Kim, J., Joo, S. H., Kim, Y. J., Zhang, L., Liu, Z., Wang, J. Q., Kwak, S. K., & Kim, G. (2022). Promotion of the oxygen evolution reaction: Via the reconstructed active phase of perovskite oxide. Journal of Materials Chemistry A, 10(5), 2271–2279. Figure 1

Kinetics of ethane exsolution and dissolution in bitumen

Dissolution and exsolution of gases are common in many engineering applications. Dissolution and exsolution occur across a gas-liquid interface when the equilibrium condition is disturbed. This study presents experimentally measured data on the exsolution and dissolution kinetics of ethane and bitumen (a viscous liquid) system across a temperature range of 80–140 °C and pressure differences of 0.69 and 0.35 MPa. Analytical models were adopted to estimate the exsolution and dissolution coefficients from the measured data for the ethane/bitumen system. The diffusivity values for the exsolution and dissolution processes were estimated to range from (2.65–10.48) × 10−8 m2/s and (0.73–6.18) × 10−9 m2/s, respectively, at a pressure difference of 0.69 MPa, and from (1.61–8.33) × 10−8 m2/s and (0.89–10.78) × 10−9 m2/s, respectively, at a pressure difference of 0.35 MPa. For both pressure differences, the exsolution kinetics were shown to be faster than dissolution in the ethane/bitumen system. This was also confirmed by higher activation energy for the exsolution process calculated using the Arrhenius equation. The results offer valuable insights into the kinetics of gas exsolution and dissolution, with applications in designing and optimizing processes where nonequilibrated gases and liquids are brought into contact.

An active and durable perovskite electrode with reversibly phase transition-induced exsolution for protonic ceramic cells

Protonic ceramic cells (PCCs) possess great application potential, attributed to their cleanliness and high energy conversion efficiency. However, designing active air electrodes with both high stability is challenging. Herein, we report a nanospinel-modified perovskite oxide, Nd0.5Ba0.5Mn0.7Co0.15Ni0.15O3−δ-(CoxNiy)3O4 (CNO@NBMCN), obtained by a reversibly phase transition-induced exsolution process, as a highly active and durable air electrode for PCCs. Phase-field simulations reveal the intrinsic mechanism of nanoparticles strongly pinning to the substrate in a high-temperature oxidizing environment. The CNO@NBMCN electrode exhibits remarkable low area specific resistance (0.38 Ω cm2 at 600 °C) and exceptional stability (degradation rate 0.01 % h−1). It is confirmed by soft X-ray absorption spectroscopy that the construction of the heterostructure leads to more distortion in Mn–O octahedra and weaker metal–oxygen bonds, thereby contributing to the formation of oxygen vacancies. And the exceptionally high durability supported by both fast ion surface exchange and charge transfer at triple-phase boundaries. A single cell with the CNO@NBMCN air electrode achieves outstanding performances in the fuel cell (peak power density of 1.28 W cm−2) and electrolysis modes (current density of −2.14 A cm−2 at 1.3 V), recorded at 700 °C. This work inspires innovative design concepts for robust heterogeneous electrocatalysts.

A‐Site Defect Engineering Regulates Bimetallic Exsolution in Perovskite Oxide Boosting the Performance of Li–O2 Batteries

AbstractThe application life of Lithium–oxygen (Li–O2) batteries can be significantly affected by the formation and full decomposition of the discharge product Li2O2. After exsolution, the catalyst is designed to control the morphology and crystallinity of Li2O2 enhanced reversibility. In the perovskite exsolution system, the large amount of A‐site defects are introduced to induce the activation of lattice oxygen and the formation of oxygen vacancy, and promote the bimetallic exsolution from LaxFe0.8Cu0.1Co0.1O3. When x = 0.70, the distribution density of CuCo alloy and Cu metal increases and the size is smaller. Through exsolution process, the resulting oxygen vacancy and more doped ions exsolved expose a significant number of active sites that enhance the charge transfer and catalytic activity. Therefore, the charge resistance (Rct) smaller and can be better decomposed due to the generated small‐size Li2O2 with nano‐sheet morphology. Meanwhile, theoretical calculation shows that the exsolution of the catalyst enhances the adsorption of the intermediate LiO2 that makes the surface mechanism more advantageous. The reversibility of the battery is improved, and the cycle stability reaches 195 cycles. This work can serve as a guide for the development of exsolution that directs the design of high efficiency cathode catalyst.

In situ ex-solution of CoFeRu solid solution nanoparticles from non-stoichiometric (La0.8Sr0.2)0.9Co0.1Fe0.8Ru0.1O3−δ perovskite for hydrogen gas sensor

Ex-solution process is a novel technology to grow uniformly distributed highly catalytic nanoparticles (NPs) on the surface of parent metal oxide solid support and has been recently applied to diverse engineering applications. Here, we study the effect of CoFeRu NPs which are ex-solved on the surface of Ru-doped La0.8Sr0.2Co0.1Fe0.9O3−δ (LSCF) perovskite at reduction temperature 350–550 °C. The shape and size of decorated CoFeRu NPs on the surface of the (LSCFRu, La0.8Sr0.2Co0.1Fe0.8Ru0.1O3−δ) sensing layer was studied for controlled hydrogen gas sensing. The results show that the ex-solved LSCFRu sensor leads to an enhanced gas response, long-term stability, and a smaller limit of detection (LOD=0.05 ppm) against H2 gas exposure at 450 °C. The hydrogen gas sensing properties of ex-solved LSCFRu, La0.8Sr0.2Co0.1Fe0.8Ru0.1O3−δ, is (Ra/Rg = 55) after reduction at 450 °C was enhanced to 20-folds compared to un-doped LSCF with a detection limit of 0.05 ppm. The high gas response is ascribed to the catalytic effect of uniformly embedded CoFeRu NPs ex-solved via p-to-n type transition of the LSCFRu parent oxide after reduction. The concept demonstrated here may serve in the development of potential ex-solved perovskite sensors for advanced and reliable hydrogen gas sensing.

Copper-perovskite interfacial engineering to boost deNOx activity

By adjusting the Cu doping level and calcination temperature during synthesis of a series of noble metal-free lanthanum copper manganite perovskites LaCuxMn1-xO3, we show the importance of tuning the redox chemistry for optimum steering of the catalytic activity and N2 selectivity in the catalytic reduction of NO by CO. A prerequisite is the in situ formation of an extended copper-perovskite phase boundary. The associated improvement of redox and surface properties by Cu addition leads to an optimized balance of the reduction of the catalyst in the NO+CO reaction mixture. The creation of oxygen vacancies improves the reaction kinetics and initiates the NO dissociation. Strongly dependent on the calcination temperature, the Cu/Mn ratio, the reducing agent, as well as the reaction temperature as parameters for Cu-perovskite interfacial control, surface reduction can induce partial copper exsolution, significant perovskite reduction, agglomeration of exsolved Cu particles and eventual decomposition of the catalyst structure. We show that increasing the amount of initial copper incorporated into the perovskite structure can beneficially extend the phase boundary, but exceeding the amount of copper leads to increased sintering of the copper particles at the expense of catalyst activity, especially in repeated catalytic cycles. Increasing the calcination temperature, in addition to the initial sintering of the catalyst and shifting the reaction onset temperature to higher temperatures in the first cycle, improves the reduction resistance of the catalyst. Consequently, in order to form a higher amount of phase boundary-bound active sites, stronger reducing conditions than provided by the NO+CO reaction mixture are needed. This effect can be counterbalanced by using stronger reduction agents prior to performing subsequent catalytic cycles by inducing the exsolution process.

The magma evolutional constrains on the genesis of proximal Zn skarn mineralization: A case study from the Yaojialing deposit in Tongling district, eastern China

The major factors especially the roles of the magma evolution controlling the Zn/Cu mineralization in skarn deposits are still controversial. Yaojialing is a large-sized skarn Zn polymetallic deposit (1.74 Mt Zn at 3.6 %, 30.4 t Au at 4.2 g/t and 24.8 t Cu at 0.83 %) located in the Tongling district of the Middle–Lower Yangtze belt (MLYB), both the proximal and distal areas of the deposit exhibit high Zn/Cu mineralization. The intrusions in Yaojialing primarily consist of quartz monzonite porphyry (QMP) and granodiorite porphyry (GDP), and the QMP is related to skarn mineralization. Both the QMP and GDP display relatively high (87Sr/86Sr)i values (0.707907 to 0.709390), low εNd(t) values (−9.05 to −8.17) and negative εHf(t) values (−8.51 to −11.72), suggesting that they originated from a mixed source of enriched mantle and lower crust. Both the QMP and GDP contain type I and type II amphiboles, while type III amphibole exists only in QMP. Type I amphibole is acicular crystals shape, type II amphibole is euhedral in shape and relatively large in size (0.6–2.0 mm), while type III amphibole crystallized around the margin of type II amphibole. The type I amphibole from QMP and GDP show similar calculated temperatures (948–1010 ℃), pressures (2.9–6.5 kbar, corresponding depths at 11.0 to 24.4 km), fO2 (ΔFMQ = 0.2–1.9) and H2O content (4.2–6.8 wt%). Type II amphibole crystallized at 815–941 ℃, 1.2–2.9 kbar (corresponding to depth of 4.6–11.1 km), ΔFMQ = 0.7–2.1, and 4.4–5.7 wt% H2O. Type III amphibole have a lower temperature (679–795 ℃), pressure (<0.5 kbar) and water content (2.5–4.3 wt%) but higher fO2 value (ΔFMQ = 3.1–3.8) compared to type I and type II amphiboles. Reverse zoning of plagioclase and higher Mg# (74 to 89) of type III amphibole in QMP are resulted from injection of mafic magma at shallow depths, which provide sufficient metal and favorable conditions for the formation of QMP parental magma. Modeling of magma H2O solubility indicates that QMP begins to exsolve fluid at depth of 6.2–11.1 km. Initial low oxygen fugacity and ore-forming element differential release during fluid exsolution process resulted in the high Zn/Cu mineralization at Yaojialing.

A-site-deficiency range identified for in situ exsolution from (La0.4Sr0.6)1-αTi0.95Ni0.05O3±δ electrodes for SOFC and SOEC.

Modulating the A-site deficiency is a useful method to achieve the exsolution of nanoparticles on the surface of perovskite, improving the catalytic activity. However, rules for designing the deficiency value and its roles on the structure and performance remain unclear. In this study, a wide range of A-site deficiencies of (La0.4Sr0.6)1-αTi0.95Ni0.05O3±δ (LSTN, α = 0.00, 0.13, 0.15, and 0.18) titanate perovskite materials was designed to systematically investigate their crystal structure, binding energy, oxygen vacancy concentration, exsolution process, and electrochemical performance. An extremely high conductivity (e.g., 331.75 S cm-1@800 °C, 5% H2/Ar) was obtained in parallel with enhanced catalytical activity in SOFC and SOEC modes. The A-site-deficient samples displayed a higher conductivity, oxygen vacancy concentration, and power output than the stoichiometric samples (α = 0.00). The best maximum power density of 78.74 mW cm-2 and the highest population density of 25 particles per μm2 were obtained on the deficient LSTN with α = 0.13. These findings suggest that LSTN is an exceptionally promising material for solid oxide cell (SOC) electrodes.

Plasma driven exsolution of Ca as the adjacent dechlorinated site in La0.8Ca0.2MnO3 perovskite: A highly mineralization chlorobenzene oxidation catalyst

The degradation of chlorine-containing volatile organic compounds (CVOCs) catalytic combustion technology is subject to the catalyst chlorine poisoning, which is resulted from the chlorination of active phases, even though the structural stable perovskite. The reaction between Ca species and dissociated chlorine species is demonstrated as an efficient way to inhibited chlorine poisoning of the active phase. Herein, a Ca substituted partial La prepared La0.8Ca0.2MnO3 (named as L8C2MO) perovskite was treated by 5% H2/Ar plasma driven route (the treated sample was denoted as L8C2MO-P), which was applied for the chlorobenzene oxidation removal. The integrated characterization results of XRD, XPS, HRTEM, etc. confirmed that Ca (mainly exhibited as CaCO3) was successfully exsolved from La0.8Ca0.2MnO3 and simultaneously leaved oxygen vacancies on the surficial layers. The continuous catalytic oxidation experiments illustrated that the conversion efficiency of L8C2MO was unexpectedly decreased compared with that of LaMnO3 (LMO in short) sample, while that of L8C2MO-P was nearly maintained the oxidation capacity, with approximately 12 °C of 90% chlorobenzene conversion temperature (T90) higher than that of LMO. Importantly, the CO2 and inorganic chlorine species yields were significantly enhanced for L8C2MO and L8C2MO-P. The characteristic of used samples showed a possible chlorinated Ca species formation while the status of Mn phases was hardly changed, suggesting the exsolved Ca could inhibit the poison of Mn sites by binding with dissociative chlorine species. Additionally, oxygen vacancies that generated along with Ca exsolution process was definitely contributed to the deep oxidation of chlorobenzene. The possible reaction route was also studied by in situ DRIFTS and GCMS. The work provides a potential route as in situ growth of adjacent sites to protect active phases from chlorine poison in CVOCs catalytic oxidation process.

Tailoring the A and B site of Fe-based perovskites for high selectivity in the reverse water-gas shift reaction

The reverse water-gas shift reaction (rWGS) is of particular interest as it is the first step to producing high-added-value products from carbon dioxide (CO2) and renewable hydrogen (H2), such as synthetic fuels or other chemical building blocks (e.g. methanol) through a modified Fischer-Tropsch process. However, side reactions and material deactivation issues, depending on the conditions used, still make it challenging. Efforts have been put into developing and improving scalable catalysts that can deliver high selectivity while at the same time being able to avoid deactivation through high temperature sintering and/or carbon deposition. Here we design a set of perovskite ferrites specifically tailored to the hydrogenation of CO2 via the reverse water-gas shift reaction. We tailor the oxygen vacancies, proven to play a major role in the process, by partially substituting the primary A-site element (Barium, Ba) with Praseodymium (Pr) and Samarium (Sm), and also dope the B-site with a small amount of Nickel (Ni). We also take advantage of the exsolution process and manage to produce highly selective Fe-Ni alloys that suppress the formation of any by-products, leading to up to 100% CO selectivity.

Enhancing layered perovskite ferrites with ultra-high-density nanoparticles via cobalt doping for ceramic fuel cell anode

Nanoparticles anchored on the perovskite surface have gained considerable attention for their wide-ranging applications in heterogeneous catalysis and energy conversion due to their robust and integrated structural configuration. Herein, we employ controlled Co doping to effectively enhance the nanoparticle exsolution process in layered perovskite ferrites materials. CoFe alloy nanoparticles with ultra-high-density are exsolved on the (PrBa)0.95(Fe0.8Co0.1Nb0.1)2O5+δ (PBFCN0.1) surface under reducing atmosphere, providing significant amounts of reaction sites and good durability for hydrocarbon catalysis. Under a reducing atmosphere, cobalt facilitates the reduction of iron cations within PBFCN0.1, leading to the formation of CoFe alloy nanoparticles. This formation is accompanied by a cation exchange process, wherein, with the increase in temperature, partial cobalt ions are substituted by iron. Meanwhile, Co doping significantly enhance the electrical conductivity due to the stronger covalency of the CoO bond compared with FeO bond. A single cell with the configuration of PBFCN0.1-Sm0.2Ce0.8O1.9 (SDC)|SDC|Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF)-SDC achieves an extremely low polarization resistance of 0.0163 Ω cm2 and a high peak power density of 740 mW cm−2 at 800 °C. The cell also shows stable operation for 120 h in H2 with a constant current density of 285 mA cm−2. Furthermore, employing wet C2H6 as fuel, the cell demonstrates remarkable performance, achieving peak power densities of 455 mW cm−2 at 800 °C and 320 mW cm−2 at 750 °C, marking improvements of 36% and 70% over the cell with (PrBa)0.95(Fe0.9Nb0.1)2O5+δ (PBFN)-SDC at these respective temperatures. This discovery emphasizes how temperature influences alloy nanoparticles exsolution within doped layered perovskite ferrites materials, paving the way for the development of high-performance ceramic fuel cell anodes.

Exsolution process in white dwarf stars

Context. White dwarf stars are considered to be suitable cosmic laboratories for studying the physics of dense plasma. Furthermore, the use of white dwarf stars as cosmic clocks to date stellar populations and main sequence companions demands an appropriate understanding of the physics of white dwarfs in order to provide precise ages for these stars. Aims. We aim to study exsolution in the interior of white dwarf stars, a process in which a crystallized ionic binary mixture separates into two solid solutions with different fractions of the constituents. Depending on the composition of the parent solid mixture, this process can release or absorb heat, thus leading to a delay or a speed-up of white dwarf cooling. Methods. Relying on accurate phase diagrams for exsolution, we modeled this process in hydrogen(H)-rich white dwarfs with both carbon–oxygen (CO) and oxygen–neon (ONe) core composition, with masses ranging from 0.53 to 1.29 M⊙ and from 1.10 to 1.29 M⊙, respectively. Results. Exsolution is a slow process that takes place at low luminosities (log(L/L⊙)≲ − 2.75) and effective temperatures (Teff ≲ 18 000 K) in white dwarfs. We find that exsolution begins at brighter luminosities in CO than in ONe white dwarfs of the same mass. Massive white dwarfs undergo exsolution at brighter luminosities than their lower-mass counterparts. The net effect of exsolution on white dwarf cooling times depends on the stellar mass and the exact chemical profile. For standard core chemical profiles and preferred assumptions regarding miscibility gap microphysics, the cooling delay can be as large as ∼0.35 Gyr at log(L/L⊙)∼ − 5. We neglect any chemical redistribution possibly associated with this process, which could lead to a further cooling delay. Although the chemical redistribution is known to accompany exsolution in binary solid mixtures on Earth, given the solid state of the matter, it is hard to model in a reliable way, and its effect may be postponed until very low luminosities. Conclusions. Exsolution has a marginal effect on white dwarf cooling times and, accordingly, we find no white dwarf branches associated with it on the Gaia color–magnitude diagram. However, exsolution in massive white dwarfs can alter the faint end of the white dwarf luminosity function, thus impacting white dwarf cosmochronology.

P-doped RuPd nanoparticles anchored on Y2Ru2-xPdxO7 pyrochlore oxide surface as oxygen evolution and reduction electrocatalysts for Zn-air battery

Metal-air battery technology is the most promising green technology. However, the sluggish kinetics of the oxygen evolution/reduction reaction (OER and ORR), which are key reactions in air cathode, must be improved. In this study, Pd substitution was introduced into Y2Ru2O7 pyrochlore oxides and the ratio of Pd was varied (YRPO-x). Then, P-doped RuPd nanoparticles were synthesized on Pd-substituted YRPO pyrochlore (YRPO/RuPd-P) by an in situ exsolution process to create bifunctional electrocatalysts facilitating both reactions. The uniquely designed YRPO/RuPd-P catalyst exhibited the OER overpotential and Tafel slope (Ej10 = 232 mV; Tafel slope = 37.1 mV/dec). Furthermore, YRPO/RuPd-P shows an E1/2 of 0.82 V, indicating superior ORR activity. This was further investigated by applying in a unit-cell battery system, which showed an outstanding power density (163 mW/cm2) and robust charge–discharge stability. This study proposes a novel design strategy for bifunctional electrocatalysts.

Accelerating metal nanoparticle exsolution by exploiting tolerance factor of perovskite stannate.

The octahedral symmetry in ionic crystals can play a critical role in atomic nucleation and migration during solid-solid phase transformation. Similarly, octahedron distortion, which is characterized by Goldschmidt tolerance factor, strongly influences the exsolution kinetics in the perovskite lattice framework during high-temperature annealing. However, a fundamental study on manipulating the exsolution process by octahedron distortion is still lacking. In this study, we accelerate Ni metal exsolution on the surface of perovskite stannates by increasing the [BO6] octahedron distortion in the lattices. Decreasing the A-site ionic radius (rBa2+ = 161 pm → rSr2+ = 144 pm → rCa2+ = 134 pm) increased the density of exsolved Ni nanoparticles by up to 640% (i.e., 47 particles μm-2 of Ba(Sn, Ni)O3 → 304 particles μm-2 of Ca(Sn, Ni)O3) after the identical exsolution process. Based on the theoretical calculation and experimental characterization, the decrease in crystal symmetry by octahedral distortion promoted the Ni exsolution owing to the boosted Ni migration by weakening the bond strength and generating domain boundaries. The findings highlight the importance of octahedral distortion to control atomic migration through the perovskite lattice framework and provide a strategy to tailor the density of uniformly populated nanoparticles in nanocomposite oxides for multifunctional material design.

Metal exsolution from perovskite-based anodes in solid oxide fuel cells.

Solid oxide fuel cells (SOFCs) are highly efficient and environmentally friendly devices for converting fuel into electrical energy. In this regard, metal nanoparticles (NPs) loaded onto the anode oxide play a crucial role due to their exceptional catalytic activity. NPs synthesized through exsolution exhibit excellent dispersion and stability, garnering significant attention for comprehending the exsolution process mechanism and consequently improving synthesis effectiveness. This review presents recent advancements in the exsolution process, focusing on the influence of oxygen vacancies, A-site defects, lattice strain, and phase transformation on the variation of the octahedral crystal field in perovskites. Moreover, we offer insights into future research directions to further enhance our understanding of the mechanism and achieve significant exsolution of NPs on perovskites.

How reduction temperature influences the structure of perovskite-oxide catalysts during the dry reforming of methane.

Dry reforming of methane is a promising reaction to convert CO2 and combat climate change. However, the reaction is still not feasible in large-scale industrial applications. The thermodynamic need for high temperatures and the potential of carbon deposition leads to high requirements for potential catalyst materials. As shown in previous publications, the Ni-doped perovskite-oxide Nd0.6Ca0.4Fe0.97Ni0.03O3 is a potential candidate as it can exsolve highly active Ni nanoparticles on its surface. This study focused on controlling the particle size by varying the reduction temperature. We found the optimal temperature that allows the Ni nanoparticles to exsolve while not yet enabling the formation of deactivating CaCO3. Furthermore, the exsolution process and the behaviour of the phases during the dry reforming of methane were investigated using in situ XRD measurements at the DESY beamline P02.1 at PETRA III in Hamburg. They revealed that the formed deactivated phases would, at high temperatures, form a brownmillerite phase, thus hinting at a potential self-healing mechanism of these materials.